Source file src/pkg/math/bits.go
1 // Copyright 2009 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package math 6 7 const ( 8 uvnan = 0x7FF0000000000001 9 uvinf = 0x7FF0000000000000 10 uvneginf = 0xFFF0000000000000 11 mask = 0x7FF 12 shift = 64 - 11 - 1 13 bias = 1023 14 ) 15 16 // Inf returns positive infinity if sign >= 0, negative infinity if sign < 0. 17 func Inf(sign int) float64 { 18 var v uint64 19 if sign >= 0 { 20 v = uvinf 21 } else { 22 v = uvneginf 23 } 24 return Float64frombits(v) 25 } 26 27 // NaN returns an IEEE 754 ``not-a-number'' value. 28 func NaN() float64 { return Float64frombits(uvnan) } 29 30 // IsNaN returns whether f is an IEEE 754 ``not-a-number'' value. 31 func IsNaN(f float64) (is bool) { 32 // IEEE 754 says that only NaNs satisfy f != f. 33 // To avoid the floating-point hardware, could use: 34 // x := Float64bits(f); 35 // return uint32(x>>shift)&mask == mask && x != uvinf && x != uvneginf 36 return f != f 37 } 38 39 // IsInf returns whether f is an infinity, according to sign. 40 // If sign > 0, IsInf returns whether f is positive infinity. 41 // If sign < 0, IsInf returns whether f is negative infinity. 42 // If sign == 0, IsInf returns whether f is either infinity. 43 func IsInf(f float64, sign int) bool { 44 // Test for infinity by comparing against maximum float. 45 // To avoid the floating-point hardware, could use: 46 // x := Float64bits(f); 47 // return sign >= 0 && x == uvinf || sign <= 0 && x == uvneginf; 48 return sign >= 0 && f > MaxFloat64 || sign <= 0 && f < -MaxFloat64 49 } 50 51 // normalize returns a normal number y and exponent exp 52 // satisfying x == y × 2**exp. It assumes x is finite and non-zero. 53 func normalize(x float64) (y float64, exp int) { 54 const SmallestNormal = 2.2250738585072014e-308 // 2**-1022 55 if Abs(x) < SmallestNormal { 56 return x * (1 << 52), -52 57 } 58 return x, 0 59 }